As is well known, generic screwless connection terminals which usually have clamp springs, which often are designated as cage clamp springs, have the advantage that a conductor to be electrically connected can be mounted without screwing means. Through the principle of clamping the core ends of the conductor, which basically can be a single- or multi-core electric cable with a stranded wire line, a solid wire or a conductor inserted in a core end ferrule, to a contact element, an automatic adaptation to the respective cross-section takes place. This makes it possible that one and the same connection terminal can be used for differently dimensioned flexible lines and cables. Said connection terminals are used, among other things, in electrical plug connector systems which are designed for three-phase current and/or alternating current and consist of a plug part and a coupling part or a wall socket such as, for example, connector plugs, flanged connector plugs, wall-mounted plugs, surface-mounted plugs and electrical outlets, the requirements for which are further described in the standards IEC 60309-1 and EN 60309-1, -2.
A plug connector device known from EP 1 072 067 B1 has a screwless conductor terminal accommodated in a plug connector or in a coupling. The substantially tubular connector or coupling housing made of insulating plastic comprises an inner cylindrical contact element carrier which holds the contact elements in position. Said contact element carrier of the connector housing is configured for receiving contact pins and the contact element carrier of the coupling is configured for receiving socket contacts. When mounting the conductor to the screwless connection terminal, the connector end of the cable is led through a cover which is made of insulating plastic and is connected to the plug connector or coupling housing and has a strain relief device for the cable. The core ends to be connected which are exposed beforehand are subsequently fixedly clamped to the contact elements in the contact element carrier by means of a clamp spring. Said clamp spring has a clamp opening which needs to be brought in a pretensioned release position and into which the conductor to be connected is inserted with the core end that has been stripped beforehand. Once the clamp opening of the clamp spring is subsequently closed, the core end is pulled by means of the cross-sectional area of the clamping leg of the clamp spring against the contact surface of the contact element and subsequently clamped in place whereby an electrical contact is made.
Further screwless conductor terminals using structurally identical clamp springs for clamping electrical conductors to contact elements are known. EP 1 555 724 A1 discloses e.g. a single-pole to multi-pole conductive bus bar having one or more of screwless conductor terminals, wherein said bus bar has a plurality of said aforementioned clamp springs arranged next to each other for connecting a plurality of conductors.
In case of this type of clamping, the effective clamping surface of such screwless connection terminals is limited to the profile cross-section of the clamp spring and is only a few square millimeters. As a result of this, in case of screwless connection terminals according to the prior art, there are usually high electrical contact resistances which result in excessive heat generation. These disadvantages are increasingly experienced in particular in such cases in which high electric currents, e.g. 32 A and higher, are to be transmitted. Also, a comparatively high electrical contact resistance exists at further possible contact area sections against which the conductor abuts, but does not experience any directly acting clamping force applied by the cross-sectional area of the clamping leg of a connection terminal or a clamp spring.
The electric current generally flowing through the contact resistances of a screwless connection terminal according to the prior art thus generates a significant heat quantity which has to be dissipated via the contact element. However, if high electrical currents flow through such a conductor terminal, the result is, besides an excessive heat generation, a high electrical loss and a high risk with respect to melting or fire hazard. Thus, it can principally be concluded that the field of use with respect to ampacity of screwless connection terminals, the electrical contact of which is established by means of the cross-sectional area of the clamping leg of a clamp spring, is limited.